Method of making liner

ABSTRACT

A liner for a centrifugal pump of the type made from wear resistant metal is conventional made with a step (5) in the inner surface of the liner between the junction of the side liners (2 and 3) and the volute liner (1), because of the difficulty in machining the hydraulic surface of the liner. This step (5) causes localized accelerated wear. The liner of the present invention is made with a thickening (11) of the area adjacent the joint with the side liners (2 and b 3) which thickening protrudes inwardly beyond the inner surface of the side liners (2 and 3). Upon assembly the thickening (11) is reduced to align with the inner surface of the side liners (2 and 3), to reduce localized wear on the liner.

The present invention relates to an improved centrifugal pump and inparticular to an improved liner construction for centrifugal slurrypumps and method of construction thereof and particularly to centrifugalslurry pumps wherein because of their method of construction a sharpdiscontinuity occurs on the inner surface because of the mating of theliner components.

As these pumps are used in slurry applications, hard metal orelastomeric liners are necessary to minimise wear. As the metal andelastomeric liners are required to be interchangeable, it is necessaryto make the liners of different materials with the same internal"hydraulic" shape, so that performance does not change when liners arechanged.

With hard metal liners, the only available method to conform the linerto the required dimensions until recently was by means of grinding.Grinding is slow and costly and is confined to flat surfaces, readilyaccessible to large grinding wheels. Therefore the grinding of excessmaterials from hard metal liners was restricted to the minimum.

Hard metal parts made from a casting process are difficult to controldimensionally, particularly when cores are used, as cores can shift andcause variations in casting thickness. As it is necessary that the linerand its parts must fit exactly within required tolerances in the casingas shown in FIG. 3, the outer surfaces 16 of the volute liner 1 and theouter surface 15 and 17 respectively of the throat bush 2 and frameplate liner insert 3 (as shown in FIG. 1 and 2) are machined to therequired width.

In FIG. 2 is shown a close-up of the fitting of the throat bush 2 andthe volute liner 1 in the prior art pump shown in section view in FIG.3. Because the parts are produced as cast metal liners or as mouldedelastomeric liners as is required by the medium to be pumped, it isnecessary that the mating surfaces 6 and 7 of both the volute liner 1and the throat bush 2 are produced to smooth finish to ensure accuratefitting of the mating parts. Further to fit the liners into the pumpsthe outer surfaces 15 and 16 are machined. The inner surfaces of theliner are not machined.

Because of the above considerations, it is extremely difficult to casttwo separate hard metal parts such as a volute and throat bush which,when ground and fitted together, have the inside surfaces matchingexactly.

As it was not practical to make the liner parts'inner surfaces flush,the side liners (i.e. throat bush 2 and frame plate liner insert 3) wereallowed to protrude further inwards than the inside surface 8 of thevolute liner 1 as shown in FIG. 1 to 4. This configuration is preferablefrom a wear point of view than having the inside liners thinner than thevolute liner as shown in FIG. 5.

In order that elastomeric lined pumps have the same performance as metallined pumps, the elastomeric liners are produced with the same internalshape as the metal liners, although the rubber liners can be moulded tovery much closer tolerances than metal liners.

It is known that, when slurries or liquids having entrained solids arepumped, the solids can cause wear on the parts of the pumps. Eddying andunwanted turbulence are formed near areas of the pump casing or linerwhich have abrupt discontinuity, such as steps, of the surface profile.This problem is particularly associated with the mating of the throatbush and the volute liner, and the mating of frame plate liner insertand the volute liner in pumps where components are metal (e.g., castmetal) and the respective mating surfaces require machining or the like.As shown in FIGS. 1 to 4 there is a discontinuity 4 in the form of astep 5 on the inner surface of the liner between the volute liner 1 andthe throat bush 2 and between the volute liner 1 and the frame plateliner insert 3 in prior art centrifugal slurry pumps.

This discontinuity causes eddying and turbulence around the step 5 withconsequential abrasion by the entrained solids of the volute liner andside liners, producing a high wear area, as shown in FIG. 6. The flowleaving the pump impeller enters the internal pump passageway, butbecause of the step 5 on the side liners 2 and 3, eddies can cause aconcentration of wear at the step 5 and subsequent wear on the jointfaces as shown. Thus the volute liner fails prematurely and only in alocalised area near the joints between the side liners and the voluteliner.

Because of recent advances in manufacturing techniques, machining ofhard metals is now not confined to grinding. Hard metals can be machinedby using special tooling on standard turning/boring machines.

The present invention seeks to ameliorate the above disadvantages.

In one period form the invention comprises a liner for a centrifugalslurry pump comprising:

a throat bush having an inner surface;

a volute liner having an inner surface; and

a frame plate liner insert having an inner surface, wherein said throatbush and said frame plate liner insert each mate in a respective openingin said volute liner and wherein the volute liner has a wall thickeningat and adjacent the respective openings so that the said volute linerhas its inner surfaces projecting inwardly at said opening of the innersurfaces of the said throat bush and said frame plate liner insert, whensaid volute liner, said throat bush and said frame plate liner insertare assembled and wherein said wall thickening of said volute liner atand adjacent said respective openings is reduced such that said innersurfaces of the volute liner and throat bush and said inner surfaces ofthe volute liner and the frame plate liner insert are substantiallyaligned at the area of the opening.

The present invention will now be described by way of example withreference to the accompanying drawings, in which:

FIGS. 1-6 illustrate fragmentary cross-sectional views of prior artliners;

FIG. 7 illustrates a detail of a cross-section of the volute liner atits opening according to one embodiment of the present invention;

FIG. 8 illustrates the mating of the above volute liner with a throatbush with the components suitably ground to the required sizes;

FIG. 9 illustrates a cross-sectional view of the mating of the abovevolute liner with both side liners; and

FIG. 10 illustrates the area of the opening in an elastomeric voluteliner to receive the throat bush.

As mentioned previously, because the sealing faces and the back faces ofthe volute liner, the throat bush and the frame plate liner insert haveto be machined to ensure accurate fit therebetween and accurate fit inthe pump casing, it is difficult to align the inner faces or surfaces 8and 9, and hence a discontinuity with its resultant step 5 occurs (seeFIG. 2).

As shown in FIG. 7, according to the present invention the area of theopening 10 of the volute liner is cast with a thickened protrusion 11(as shown by dotted lines).

The mating faces or surfaces 6 and 7 and the back faces 15 and 16 of thevolute liner and throat bush are machined to the required degree suchthat the parts fit together in sealing relationship. This leaves a smallprojection 13 on the inner surface of the volute liner 1.

This is then removed when the final fitting of the throat bush to theliner has occurred to form a smooth transition 14 from the inner surface9 of throat bush 2 to the inner surface 8 of the volute liner 1, asshown in FIG. 8 without weakening the liner due to reduction inthickness. A similar procedure is carried out with frame plate linerinsert opening to produce an alignment as shown in FIG. 9.

A similar shaped thickening 15 is used with elastomeric volute liners 11as shown in FIG. 10.

However, as elastomeric material can be moulded more accurately thanhard metal, no machining is necessary. Thus the volute liner has beenthickened adjacent its joint with the side liners producing a smoothalignment of the volute liner and side liners inner surfaces.

It should be obvious to people skilled in the art that variation andmodifications can be made to the above without departing from the scopeor the spirit of the present invention.

I claim:
 1. A method of assembly a liner for a centrifugal slurry pumpcomprising;(i) a throat bush having an inner surface and an outersurface; (ii) a volute liner having an inner surface and an outersurface and two opposed openings, the volute liner having a wallthickening surrounding each opening on the inner surface of said voluteliner; and (iii) a frame plate liner insert having an inner surface andan outer surface;said method comprising the steps of: (A) inserting thethroat bush into one of the openings of the liner into its assembledposition, whereby the volute liner has the respective wall thickeningprojecting inwardly at the one opening beyond the inner surface of thethroat bush; (B) reducing the inner surface of the volute liner adjacentthe one opening until the inner surfaces of the volute liner and throatbush are substantially aligned around the one opening; (C) inserting theframe plate liner insert into the other of the openings of the voluteliner into its assembled position, whereby the volute liner has itsrespective wall thickening projecting inwardly at the other openingbeyond the inner surface of the frame plate liner insert; and (D)reducing the inner surface of the volute liner adjacent the otheropening until the inner surfaces of the volute liner and frame plateliner insert are substantially aligned around the other opening.
 2. Themethod of claim 1 comprising the additional steps of machining the outersurfaces of the volute liner, throat bush and frame plate liner insertsuch that the liner is of sufficient width to fit within a casing of thepump.
 3. The method of claim 2 wherein the throat bush, volute liner,and frame plate liner insert are made of hard metal.